Circuit breaker



July 14, 1 936. w, A. ATwooD CIRCUIT BREAKER Filed April 25, 1935 2 Sheets-Sheet l III 2/ Inventor: Winfield A. Atwood,

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July 14, 1936. w.-A. ATwooD CIRCUIT BREAKER Filed April 25, 1935 2 Sheets-Sheet 2 lnvertr: Winfield A. Atwood,

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Patented 'July 1.4, 1936 PATENT 'oFFlcE I 2,047,816 omcorr BREAKER Winfieldy A. twood,- Yeadon, Pa., assigner to General-Electric Company, a corporation of New York Application April 25, 1935, Serial No. 18,138

12 Claims.

My invention relates to circuit breakers, more particularly toycircuit breakers of the trip-free type in which the circuit controlling contacts are manually operable Abetween open and closed circuit positions andare automatically operable to open circuit position upon the occurrence of predeterminedabnormal current conditions, and has l for an object the provision of a circuit breaker of this type which is simple and reliable in its operation and inexpensive to construct.

It hasheretofore been proposed to provide, circuit breakers of this general type with suitable explosion-proof, arc extinguishing devices so as to combine the protective features of a fuse and the ladvantages of a manually operable switch, and such circuit breakers have found considerable application in the control of distribution and feeder circuits. circuits of this type, especially in industrial applications, the circuit breaker is often required t carry normal currents of considerable magnitude and to interrupt extremely large currents in case a fault or short circuit occurs in the system. .'I'he circuit breaker must therefore be provided with conducting and interrupting elements of `con siderable size and the circuit breaker operating mechanism must be strong and rugged, which necessitates the use of heavy operating springs.

The necessity for-a rugged operating mechanism and consequently a rugged supporting arrangement is augmented by the -desirability of employing multipole circuit breakers in installations of this type, the circuit breaker usuallybelng provided with a single operating mechanism for opening and closing all of the circuits. Much is yet to be desired in a circuit breaker of this type which is strong and rugged enough to withstand the severe operating conditions encountered yand which will quickly interrupt currents of considerable magnitude without loud explosions or destructivearcing., Accordingly, it is a further object ofmy invention to provide a heavy duty circuit breaker of this type which is strong and rugged in its construction and operation.

In carrying out my invention in one form, I provide a circuit breaker comprising relatively movable contacts and an operating mechanism therefor which includes a manually operable mechanism of rugged construction for moving the contacts between open and closed circuit positions with a snap action, and current responsive means including a normally' latched tripping arm biasedby suitable trippingA springs for operating the' contacts to-.open circuit position upon the occurrence of abnormal current conditions.

More speciiically, I provide a. multipolev circuit When applied to the control of reliable in its 1 mediate the ends of each compartment. Conductor bars secured to the base so as to reinforce the same extend from the opposite ends of each compartment to the crosswall and a movable bridging member is arranged to span the crosswall for controlling the main circuit through each pole of the circuit breaker. Each bridging member carries an arcing contact arranged to provide an intermediate shunt circuit therefor, and each pole circuit of the circuit breaker includesan arc extinguishing device of the compression chamber type, the relatively reciprocal contacts of which are connected in parallel circuit relation with the bridging member and the intermediate shunt circuit When the circuit breaker is in closed circuit position. A manually and automatically operable mechanism is also provided, which is arranged to operate all of the bridging members, the intermediate shunt contacts and the reciprocal contacts between open and closed circuit positions in-predetermined sequence to prevent arcing at the main bridging contacts and to cause the nal circuit-breaking action to take place within4 the explosion-proof compression chamber. e

For a more complete understanding of my invention, reference should now be had to the drawings in Which-Fig. 1 is a plan view of a circuit breaker embodying my invention, the cover of the circuit breaker and certain parts thereof being removed to show the Aoperating mechanism; Fig. 2 is a sectional view taken along line -2-2 of Fig. 1; Fig. 3 is a detailed sectional view taken along line 3-3 of Fig. 2; Fig. 4 is a plan view of theinsulating support shown in Fig. 3 with the compression chamber removed; Figs. 5 and 6 are-frag mentary sectional views of the operating mecha- .nism of the circuit breaker in diierent operating and with aplurality of intermediate walls I2, I3 and I4 arranged to forma plurality of conductor receiving compartments extendingA lengthwise of the base. Each of the walls I2 extends from the uppermost end of the circuit breaker as viewed in Figs,l 1 and 2, to a point adjacent one of a pair ofbearing blocks I5, the purpose of which will be' fully set forth later; each of the walls I 3v extends from one of the bearing blocks I5 to a vpoint adjacent a unitary trip device indicated generally by the reference numeral I6, and each of the walls I4 extends from the lowermost end of the circuit breaker to a point adjacent the other eide of the trip device ls. It wiube observed "that the trip device I6, the construction and operation of which will be fully described later, includes a subbase I1 provided with a pair of walls I8 arranged substantially in alignment with the walls I3 and I4. Intermediate the ends of each conductor receiving compartment, I provide a crosswall I9 formed integrally with the base I6. Each conductor 'receiving compartment is provided at its opposite ends with the terminal members 20 and 2I respectively and the arrangement of the conductor members and the circuit controlling contacts for completing an electric circuit therebetween being the same in each compartment, only one such arrangement Willbe described.

Extending from the terminal member 20 along the base I0 to the crosswall I9, I provide a conductor bar 22 which is rigidly fastenedto the base IU in any suitable manner, as by the screws 23 adjacent the opposite ends thereof, and connected to the terminal member 20 by a bolt 24. Disposed on the opposite side of the crosswall I9 and extending therefrom along the base I0 to the trip device I6, is a second conductor bar 25 also rigidly fastened to the base, as by the screws 26 and 26a adjacent the opposite ends thereof. It will be observed that the' trip device I6 includes a pair of conductors 21 and 28 which are respectively connected to one end of the conductor bar 25 by the screw 26al and to the terminal 2I by a bolt 29. The respective ends of the conductor bars 22 and 25 which are disposed adjacent the cross-wall I9 are provided with contact portions 30, and a movable bridging member 3| carryingcooperating contact portions 32 is arranged to span the crosswall I9, the contact portions 30 and 32 being preferably formed of silver or some other suitable low resistance material. A

The main current circuit for each pole of the circuit breaker extends from one of the terminals 2U through one of the conductor bars 22, the associatedv bridging member 3|, one of the con'- ductor bars 25 and through the trip device by way of the conductors 21 and 28 to one of the terminals 2l, and it Will be .observed that the conductor bars 22 and 25 are arranged to reinforce and strengthen the base I0.

Each of the bridging members nests within the legs of a U-shaped carrier 33 formed on one arm of a bifurcated lever 34, and is supported by a bolt 35 extending therethrough, a plurality of springs v36 being arranged in aligned recesses in the bridging member and the carrier to provide uniform contact pressure. In order to reduce blistering and arcing at the silver contacts 3U and 32, each bridging member is provided with an arcing tip or contact 31 secured to one end of a conducting spring 38 mounted in a slot 39 in the carrier 33 and secured thereto by a rivet 40. As shown, the end of the spring 38, remote' from the tip 31 is electrically connected to the conductor bar 25, and the tip 31is arranged to engage the conductor bar 22 to provide a shunt circuit around the bridging member 3 I, the conductingspring 38 beingfarranged -so that when the bifurcated lever 34 is operated to move the vbridging member to its open circuit position, the tip 31 will not be disengaged from the conductor bar 22 until after the contacts 30 and 32 have each pole of the circuit breaker is provided with an arc extinguishing device connected in parallel circuit relation with the bridging member 3|, which device is preferably of the type described and claimed in a copending application of Ludwig S. Walle, Serial No. 4,448, led February 1, 1935, which application is assigned to the same assignee as the present invention. For the purposes of the present invention this arc extinguishing device may be described as comprising a cylinder 4I which forms the body portion of a compression chamber and which is secured in any ,suitable mannen'as by the screws 42 (Figs. 3 and 4), to an insulating support 43 which is fastened to the y conductor bar 22 by a plurality of screws 44.

Within the eyiinder 4| is disposed a cylindricalA liner 45 of kerosene-free fiber surrounding a xed contact 46 and a reciprocal contact 41. The fixed contact 46'is electrically connected to the conductor bar 22 by means of an L-shaped conductor 48, one leg of which is rigidly fastened to thel conductor 22, and the xed contact 46 is insulated from the cylinder 4I by a plurality of insulating bushings 49 and 56 and an insulating washer 5I. It will be apparent that when the nut 52 is tightcned down on the threaded end of the xed contact 46, the insulating members` 49, 50 and 5I will be wedged tightly together by an enlarged shoulder 53 formed on the fixed contact 46 and by a wedge-shaped flange 54 on the cylinder 4I to form a gas-tight closure for the xed contact end of the cylinder and to vform a rigid support for the fixed contact. A sealing washer 55 preferably formed of soft copper is provided surrounding the enlarged portion 53 of the xed contact, which washer will be tightly wedged into engagement with the cylindrical liner 45 to assist in gas-tightly sealing this end of the cylinder 4I.

The movable contact -end of the cylinder 4I is provided with a cylindrical cap 56 Which threadedly engages the cylinder 4I and is provided with a sealing gasket 51. Supported by the cap 56, is a plug 58 in which the movable contact 41 is slidably journaled and which is provided with a 'skirt portion 59 for directingsuch gases, if any,

as escape alongtthe movable contact 41 during movement of thecontact to its open circuit position, away from the bridging member 3I and the contacts associated therewith. In. order to provide for snap action of the movable contact 41 While at the saine time substantially sealing the compression chamber formed by the cylinder 4I and its end closures, I provide a'pair of sealing washers 60 of. leather or other suitable material.- Further sealing means, for gas-tightly sealing the compression chamber when the movable contact 41 is in its open circuit position, are provided and in order that the final circuit-breaking action may take place within the compression chamber so as to prevent arcing at the bridging member, the other arm of thebifurcated operating lever 34 is connected to the reciprocatingcontact 41 by means of a resilient lost-motion connection which includes a pin 65 carried by the 75 bifurcated lever and extending through a slot 86 in the extension 63, a'suitable spring 81 being arranged within the extension 83 with its respective ends bearing against the movable contact 41 and the pin 65.

As hereinbefore mentioned, it is desirable that the nal circuit-breaking action shall occur within the compression chamber and accordingly, the

lost-motion connection between the bifurcated operating lever 34 and the reciprocating contact 41 isso proportioned that when the bifurcated lever 34 is moved between open and closed circuit positions, the circuit through the compression chamber will be 4opened subsequent to the intermediate shunt circuit through the arcing tip 31 and will be closed prior tothe closingof the intermediate shunt circuit.

It will be remembered that the bridging member circuit, the intermediate shunt circuit and the compression chamber circuit arelidentical in `each conductor receiving compartment of the circuit breaker and in order that all of the poles of the circuit breaker mayV be simultaneously opy. erated `by a single operating mechanism, I pro-l vide an insulated crossbar 88 which extends across the three poles of the circuit breaker and is journaled in the before-mentioned bearing blocks I5. Each of the .bifurcated members 34 is provided with a clamping portion 69 which' encircles t-he crossbar 68 and is tightly clampedthereto by means of screws 10.

Arranged in one of the conductor receivingl compartments adjacent the crossbar'68, a rugged operating mechanism is provided for operating the crossbar and all of the contacts associated therewithbetween open and closed circuit positions with a snap action. As may be seen best by reference to Fig. 8, this operating mechanism comprises a U-shaped frame 1| which is sup- 40'ported on the conductor bar 25 and fastened thereto in any suitable manner. Pivotally mounted on a pin 12 carried by the frame 1| is an operating element 13 provided with an insulating operating handle 14 arranged to extend through a suitable aperture 15 inthe circuit breaker cover 18.- The operating element 13 nests Within the U-shaped frame 1| and is provided with the portion 11 extending laterally therebeyond. Connected between the extending portions 11 of the operating element 13 and an operating pin 18 the arrangement and function of Which'will be more fully described, is a, pair of overcenter spring devices each of which comprises a U- shaped member 19 pivotally connected to the`pin 18, and a yoke member 80 pivotally engaging one of the extending portions 11. A pair of plunger rods 8| which are supported by the yoke 88, slidably extend through apertures in the' end of the U-shaped member 19 and carry a bearing plate 82 nested "between'the legs of the' member 19.

`Each plunger rod 8| is surrounded by a compression spring 83 the opposite ends'of which respectively bear againstI the end of the U-shaped mem- Iber 19 and the plate 82. It will be observed that the plate 82 is guided by the legs of the member 19 and that the compression springs 83, which are arrangedvto resist relativel move- In heavy duty circuit breakers of this type, the operating mechanism should be arranged to proy vide a contact pressure of considerable magnitude'at the end of the closing stroke and accordi ingly, I prefer to employ an operating mecha- 5 nism of the general ytype described and claimed in a copending application of Charles H. Hill, Serial No. 18,127, illed April 25, 1935,' which application is assigned to the same assignee as the present invention. `l0

'I'his operating mechanism, in the embodiment here shown includes in addition to the operating element 13 and the overcenter spring devices, a

, pair of spaced parallel arms 84 pivoted on the -ing the above-mentioned operating pin 18, the44 yrespective endsi of which extend through slots t 86 in the frame 1| and are engaged by the -over- 20 center spring devices. Connectedbetween the operating pin 18 and one of the bifurcated opverating levers 34 is a .toggle comprising a linkL 81, one end *of which engages the bifurcated' lever 34 and the other .end of which .is pivotedy 25 to a second link 88 which is pivotally supported onta pin 89 and provided witha slot 90 through which the operating pin 18 extends. ,The link 88 as shown is a. substantially triangular or three-point link and acts as a crank to make 30 and break the. toggle when the operating pin`18 is moved bythe overcenter spring devices.I As shown in Fig. '7, suitable cylindrical spacers 90a .are provided for centering the link 88 relative to the frame 1|, and preventing the link from 35 sliding axially of the pin 89. In Fig. 2, the circuit breaker is shown in the closed circuit position, and it will be apparent that when the Aoperating handle 14 is moved downwardly to its lowermost positiorr in a di-'40 crank lever 88 about .its pivot 89 to break theM toggle and movethe crossbar 68. and the circuit` breaker contacts connected thereto to open circuit position. Similarly, the circuit breaker may 50 be vclosed by moving the operating handle 14Min a direction away from `the trip 7device I8 toits uppermost, position, the overcenter spring devices being eiective 'whenv carried overcenter thereby to operate the crank lever 88 to the closed 55 circuit position shown in Fig. 2.A l l The circuit breaker is also adapted for automatic operation to open the circuit upon the occurrence of` predetermined abnormal` current conditionsand accordingly, the operating mech- 60 anism is provided with a pivoted tripping member 9| and a. pair of tripping Ksprings 92 the operation of which is controlled by the trip device |6 in a manner to be more fully described. The Itrip device I 6 includes alatchI 93 arranged 65 normally toengage a latch linger 94 carried by one end of the tripping member 9|, the other fend. of the'tripping member 9| being pivotally supported on the pin 12. Intermediate its ends ,la

`tl'ie' tripping member 9| is provided with a pin .95, each extending end of which carrlesa bearing plate 96 arranged to engage one end of oneplungers and springs maybe employed to bta'inx'of the tripping springs 9.2. the opposite ends ,of

the `desired pull.

hich rest in countersunk depressions 91'in the 175 y conductor bar 25. Each bearing plate 96 carries aguide rod 98 which extends through the associated tripping spring 92 into a hole 99 which extends through the conductor bar 25 and intov `A circuit breaker, sho-wn in Fig. 2, it will Ybe seen 'A that the cross member 85 which extends between the parallel arms 84 is engaged by an extending portion |00 on the tripping member 9|. Upon the occurrence of abnormal current conditions, the latch 93 of the trip device I6 will be moved in a manner to be fully described, to release the latch finger 94 whereupon the tripping springs 92 will quickly move the tripping member 9| about the pivot '|2 in a clockwise direction as viewed lin the drawings to thev position shown in Fig. 6, thereby moving the arms 84 and the operating pin 18 carried thereby to the toggle breaking position shown lin Fig. 6 against the force exerted by the over-center .spring devices, to move thecross'bar 68 and the circuit breaker contacts connected thereto to open circuit position.

In order to' reclose the circuit breaker after an automatic operation to open circuit position, it is necessary first to rmove the handle 'M from the position shown in Fig. 6 to the position shown in Fig.`5, the operating element E3 to which the operating handle 14 is fastened being provided with a portion |0| which is arranged to engage a cooperating portion |02 on the tripping member 9|, to return the tripping member to the latched position shown in Fig. 5. VThe circuit breaker contacts may now be closed by moving the handle 74 to its uppermost position shown in Fig. 2 as hereinbefore described.

Any suitable trip device may be provided for rcleasably latching the tripping member 9i in itsnormal position against the bias vexerted by the tripping springs 92 and for releasing the tripping member upon the occurrence of abnormal current conditions.y The force exerted by the tripping springs '92, however, is of considerable magnitude and accordinglyl prefer to use a rugged trip device of the type described and claimed in a copending application of John L. Lappin Serial No. 4,659, filed February 2, 1935, entitled Circuit breakers which application is assigned to the same assignee as the present invention.

This trip device which has been previously referred to as including the subbase il and the spaced walls i8, may be described for the purposes of the present application as comprising a frame supported centrally of the subbase ll having a pair of spaced walls |03 between which are supported a latch plate |04 pivoted at MD5,`

'a U-shaped impact member |06 pivoted at [lill and a U-shaped reset member |06 pivoted at l09. The latch plate |04'carries the previously referred to latch 93, and the yoke portion of the U-shaped impact member M16 is overturned to provide a striking surface i06a for engaging a` portion of the latch plate to impart a hammerlike lblow thereto. Each leg of the impact member |06 carries a pin H0 extending through a slot in one of the supporting walls |03 and arranged to engage a cam finger provided on the U-shaped reset member |08, the yoke portion of which is interposed in the path of the tripping member 9|. The impact member |06 'is normally held in the position shownin Fig. 2 by a pivoted trip bar ||2 which extends across the three conductor receiving compartments of the .which is fastened to and adapted to be heated normal position.`

circuit breaker and is normally biased by the spring 3 into engagement with a finger ||4 carried by the impact member.

Associated with the conductors in each conductor receiving compartment of the circuit break- 5 er are a thermal and a magnetic device for moving the trip bar ||2 about its pivot to release the impact member |06. Each thermal device comprises a bimetallic element ||5, one end 'of by a heater strip H6, the ends of which are respectively connected to the previously referred to conductors 21 and 28. The other end of the bimetallic element |5 isarranged adjacent an adjustable insulatingbutton and adapted to engage the button to move the trip bar I2 about its pivot upon the occurrence of an overload current of suflicient magnitude and duration to ex the bimetallic element.

Each of the magnetic devices comprises a U- shaped magnetic member |8 which partially encircles the'conductor 28 so that a magnetic flux will be induced in the member I8 upon the flow of current through the conductor. Arranged adjacent the U-shaped magnetic members |||lv is a common armature ||9 which extends across the three conductor receiving compartments and is provided with an extending nger '|20 arranged to engage the pivoted trip bar ||2 to move the same upon the occurrence of a suf- 30 ciently high overload in one or more of thecircuit breaker poles to cause the armature to be attracted by one or more of the U-shaped magnetsii8.

It will be apparent that upon the occurrence of abnormal current conditions, the trip bar ||2 will be move-d either by the thermal or by the magnetic means, depending upon the character of `the abnormal condition, to release the impact member |06 for operation by suitable biasing springs l2! to strike the latch plate |00 a hammerlike blow and release the tripping member 9H. When the tripping bar 9| is moved to tripping position by the tripping springs 92, the U- shaped reset member |08 will be released for operation by suitable resetting springs lZZ (Fig. l)

to cause the cam ngers ill to engage the pins extending from the U-shaped impact member |06 in order to return the impact member to its While I have shown a particular embodiment of my invention, -it will be understood, of course, that I do not wish to be limited thereto since modications may be made and l, therefore, contemplate by the appended claims to cover any such modications as fall Within the true spirit and yscope of my invention.

What I. claim as new and desire to secure by Letters Patent of the United States, is:

1`. A circuit breaker comprising a base formed 60 of molded insulation material having wall portions extending substantially the lengththereof to form a conductor receiving compartment, a crosswall intermediate the ends of said compartment, terminal members adjacent the respective ends of said compartment, rigid conductor bars arranged in said compartment extending along said base from each of said terminal members to said crosswall, means for securing said conductor bars to said base to reinforce the same, a movable bridging member for spanning 4said crosswall,

said bridging member cooperating with the ends of said. conductor bars -adjacent said crosswall tion, and means for moving said bridging mem-y ber between open and closed circuit positions.

2. A circuit breaker comprising a base formed o f molded insulation material having wall portions extending substantially the length thereof to form a conductor receiving compartment, a crosswall intermediate the ends of said compartment, `terminal members adjacent the respective ends ofsaid compartment, rigid conductor bars arranged in said compartment fastened to said base and extending therealong from each of said terminal members to said crosswall, the strength and rigidity of said conductor bars serving to reinforce said base throughout substantially the entire length of the base, fixed contact members carried by said conductor bars adjacent said crosswall, a bridging member spanning said cross- Wall movable between open and closed circuit positions, contact portions carried b y said bridging member arranged to engage said fixed contacts when said bridging member is in closed `circuit position, and means for moving said bridging -member between said open and closed circuit positions.

3. A multipole circuit breaker comprising a base having a plurality of wall portions extending lengthwise thereof to form individual pole compartmentsand a cross wall intermediate the ends yof each compartment, terminal members adjacent the respective'ends of each compartment,

*rigid conductor bars arranged in each compartment extending along said base from each of said terminal members tosaid crosswall, means for securing said conductor bars to said baseto reinforce said base throughout substantially the en- "tirev length thereof, movable bridging members disposed in said compartments for spanning said crosswall, each of said bridging members being arranged to cooperate with a pair of said conductor bars.' adjacent said crosswall to, complete a circuit between said terminals in each compartment'when said bridging members are in one position, and operating mear/is for moving.y all ofv said bridging members 'between open and closed circuit positions. J

4.V A multipole circuit breaker comprising a base having ay plurality of wall portions extend- V' ing lengthwise thereof to form individual conductor receiving compartments and a crosswall intermediate theends of each compartment, ter` minal members supported adjacent the respective ends of each compartment, rigid conductor barsl arrange in each compartment extending along said b e from each of said terminal members to said crosswall, means for securing said conductor bars to said base to reinforce the same throughout substantially the entire length thereof, xed contact members carried by' said conductor bars adjacent said crosswall, a movable bridging member disposed in each of said compartments spanning said crosswalls, each of said bridging members carrying contacts arranged to cooperate with a pair of said fixed contacts to complete a circuit between said terminals in each compartment, and operating means for moving all of said bridging members between open and closed circuit posi-l tions. A

5. A cir'cuit breaker comprising a base. having wall portions extending substantially the length thereof to form a conductor receiving compartment, a crosswall intermediate the ends of said tion, a compression-chamber, arc-extinguishing device provided with a pair of relatively reciprocal contacts, circuit connections for connecting said reciprocal contacts in parallel circuit relation with said bridging member, and means for operating said reciprocal contacts and said bridging member between .open and closed circuit positions in predetermined sequence whereby 'the iinal circuit-breaking action occurs in said arc-extinguishing device. I

6. A circuit breaker comprising a base having Wall portions extending substantially the length thereof to form a conductor receiving compartment, a crosswall intermediate the ends of said compartment, terminal members adjacent the respective ends of said compartment, conductor bars arranged in said compartment extending along saidv base from each of said terminal members to said c rosswall,v a bridging member spanning said crosswall and -movable between open and closed circuit positions, said bridging member cooperating withthe ends of` said conductor bars adjacent said crosswall to complete an electric circuit between said 'terminals when saidbridg'- ing member is vin said closed circuit position, means including a contact resiliently supported from said bridging member and engageable with one o f said conductor bars when said bridging member is in said closed circuit position for establishing ashunt circuit about said bridging member, said resiliently supported contact being y arranged to maintain said shunt circuit until after said bridging member is moved out of cooperating relation with said conductor bars, a compression-chamber, arc-extinguishing device provided with a pair of relatively reciprocal contacts, circuit connections for connecting said reciprocalV contacts in parallel circuit relation with said bridging member and said shunt circuit, and- 7. A circuit breaker comprising a base having wall portions extending substantially the length` thereof to form-a conductor receiving compart- `l"ment, a crosswall intermediate the ends of said compartment, terminal members adjacent the respective ends of said compartment, `conductor bars arranged in said compartment extending along ".said base from each of said terminal.

members to said crosswall, a bridging member spanning said crosswall and movable between Y open and'closed circuit positions, said bridging member cooperating with the ends of said conductor' bars adjacent said crosswall to complete an electric circuit between said terminals when said bridging member is in -said closed circuit position, an arc-extinguishing chamber insulatedly supported on one of said conductor bars,

ja fixed contact in said chamber electrically connected to one of said conductor bars, a. reciprocal contact extending through a wall oi said i chamber for cooperation with said fixed contact, said reciprocal contact 'being electrically convnected to said other conductor bar to form a yshunt circuit around said bridging' member and a common operating mechanism for -moving said reciprocal contact ,and said bridging member between open andclosed circuit position, said operating mechanism being arranged to move said bridging member to open circuitl position prior to movement of said reciprocal contact to.

'- ment, a crosswall intermediate the ends of said bars, an arc-extinguishing chamber insulatedly compartment, terminal members adjacent the respective ends of 'said compartment, conductor bars arranged in said compartment extending along said base from each of said terminal mem bers to said crosswall, a bridging member spanning said crosswall and movable betweenopen and`closed circuit positions, said bridging member cooperating `with the ends of said conductor barsadjacent saidl crosswall -to complete an electric circuit Ybetweensaid terminals when said bridging" member is in said closed circuit position, means including a contact4 resiliently supported from said bridging member and engageable with oneY of said conductor bars when said bridging member is in said closed circuit position for `establishing a shunt -circuit about said bridging member, said resiliently supported contact being arranged to maintain said shunt circuit until aiter said bridging member is moved out of cooperating relation with said conductor supported on one of said conductor bars, a xed contact in said` chamber electrically connected to one of said conductor bars, a reciprocal contactextending through a wall of said chamber for cooperation with said fixed contact, said reciprocal contact being electrically connected to said other conductor bar to form a second shunt circuit around said bridging `member and a common operating mechanism for moving .said reciprocal contact and said bridging member between open and closed circuit position, said operating mechanism being arranged to move said bridging member and said resiliently mounted contact to open circuit position prior to movement of Vsaid reciprocal contact to open circuit position whereby the nal circuit-breakin g action` occurs in said' arc-extinguishing chamber. i

9. A multipole circuit breaker comprising a base having a plurality of wall portions extending lengthwise thereof to form individual pole compartments and a crosswall intermediate the ends of each compartment,y terminal members adjacent the respective ends of each compartment, conductor bars arranged in each compartment extending along said base from each of said terminal members to said crosswall, movable bridging members disposed in said compartments for spanning said crosswall, each of said bridging Vmembers being arranged to cooperate withra pair of said conductor bars adjacent saidcrosswall to complete a circuit' between said terminalsjin each compartment when said bridging members are'in one position, arcextinguishing chambersdisposed in each compartment, a pair of relatively reciprocal contacts associated with each of said chambers;

means for connecting each pair of said reciprocal contacts in parallel circuit relation with one of said bridging members, and means for 'oper--y ating all of said pairs of reciprocaly contactsY and said bridging members between open and I closed circuit positions in, predetermined sequence whereby the iinal circuit breaking action in each compartment occurs in said arc-extinguishing chambers.

10. A multipole circuit breaker comprising a base having a plurality of wall portions extending lengthwise thereof to form individual pole compartments and a crosswall intermediate the ends of each compartment, terminal members adjacent. the respective ends of each compartment, conductor bars arranged in each compartment extending along said basey from each of said terminal members to said crosswall, movable bridging members disposed in said compartments for spanning said crosswall, each of said bridging members being arranged to cooperate with a pair of said conductor bars adjacent said crosswallr to complete a circuit between said terminals in each said bridging members are in 20- compartment when one position, arc-extinguishing chambers disposed in said compartments and insulatedly supported adjacent said conductor bars, each of said chambers ,containing a fixed contact electrically connected to a conductor bar and a reciprocal 25 contact extending through a wall thereof, each of said reciprocal contacts being electrically con- `rnected to another conductor bar to form a shunt circuit in each compartment in parallel circuit relation with said bridging members, and a single `operating mechanism for moving all of said bridging members and said reciprocal contacts between open and closed circuit position, said mechanism being arranged to move said bridging members to open circuit position prior contacts, whereby the final circuit breaking action occurs in said arc-extinguishing chambers.

1l. In a circuit breaker having a movable contact, an operating mechanism therefor comprising a movable voperating member, overcenter spring means for operating said contact between two positions with a snap action when said operating member is moved relative thereto comprising a pair of relatively movable members respectively operatively connected to said operating member and to said' movable contact, one of said members comprising a frame and the other of said members comprising a yoke, a plurality of said plate.

12. In a circuit breaker having a movable contact, an operating mechanism therefor comprising a pivoted operating member, overcenter spring means for` operating said contact between two positions with a snap action when said operating .member is moved about its pivot comprising a pair of relatively movable members respectively operatively connected to said operating member and to said contact, one of said members comprising a U-shaped frame and the other of said members comprising a yokeJ a plurality of spaced parallel plungers` carried by said yoke slidably journaled in the end of said U-shaped frame, a plate carried by the portions of said plungers within said U-shaped U-shaped frame serving as Iguides for said plate, and compression spring means disposed'about said plungers between said plate and said end of said U-shaped frame..

to said reciprocal 35 frame, theolegs of 4said 70 A. A'i'woon. 75 

